1. Field of the Invention
The present invention relates to workpiece fixturing devices adapted for moving a workpiece surface and tool means in predetermined relation to one another and, more particularly, to such devices capable of moving a workpiece circumference or girth having no rotational symmetry in prescribed relation to tool means.
2. Description of the Prior Art
Laser welding is a rapidly developing technique for joining metal parts together to form useful products. In laser welding, it is important that the laser beam be focused properly on the workpiece surfaces being joined. If the focus of the beam changes during welding, numerous problems can arise, not the least of which is that a faulty weld is produced due to improper heating of the surfaces. In laser welding parts having rotational symmetry, for example, such as cylindrical tubes, there is usually little difficulty in maintaining proper beam focusing since the parts can be rotated about their axes at a fixed distance from the lens which focuses the laser beam. Once focused, the laser beam is caused to travel around the joint simply by rotating the parts. However, in welding parts having no rotational symmetry, the problem of maintaining proper beam focusing on the workpiece surfaces has been severe and has limited the application of laser welding in production applications.
An example of the problem encountered in laser welding parts having no rotational symmetry is the gas impingement tube which is inserted in certain gas turbine engine blades to direct cooling air therethrough. A typical impingement tube comprises an elongated section having an approximate airfoil shape and a wedge shaped section, the sections having an oval-like girth or cross-section where they are to be joined together, FIGS. 1 and 2. In the past, the oval-like girth joint around the tube sections has been welded by electron beam techniques, the more or less planar portions of the joint being machine-welded while the radial portions are made manually. Of course, this welding technique is not only time consuming but also requires numerous weld dressing steps during the operation. Attempts to laser weld the complete girth joint have failed due to inability in maintaining proper focusing of the beam as it travels from the planar portions of the weld to the radial portions and also inability in maintaining the proper angle of incidence of the beam on the surfaces as it moves thereacross.